1. Field of the Invention
This invention relates to a process for the preparation of ortho-aminobenzotrifluoride from benzotrifluoride.
2. Description of the Prior Art
Ortho-aminobenzotrifluoride (OABT) is a valuable intermediate product useful in the manufacture of important products in various fields such as dyestuffs, herbicides and the like. A number of prior art methods have been disclosed for the preparation of OABT. Most industrial production of OABT has resulted from recovering small quantities of by-product OABT in the production of meta-aminobenzotrifluoride. Nitration of benzotrifluoride produces a mixture of nitro trifluoromethylbenzenes, containing only about 8 to 10% of the 2-nitrotrifluoromethylbenzene isomer. Upon reduction of the mixture OABT is obtained in yields of 8 to 10%.
Various other complicated pathways for the more specific production of OABT have been described in the literature. See Tetrahedron 8, p. 67 (1960) which illustrates a lengthy series of steps beginning with 3-acetamidotrifluoromethylbenzene. Another described procedure involves hydrolysis and Hoffmann rearrangement of 2-trifluoromethylbenzonitrile after side chain chlorination and subsequent fluorination of 2-methylbenzonitrile with SbF.sub.3. See Z. Obsch. Chim. 23, 988 (1953). OABT production employing o-toluidine as the starting point has also been described. See German Patent 627,371 and U.K. Patent 459,890. In this process the amino group in o-toluidine is protected by acylation with phthalic acid followed by chlorination and subsequent fluorination of the CH.sub.3 substituent. OABT is obtained upon hydrolysis of the protective acyl group.
Each of the individual steps of the overall process of the present invention (i.e., halogenation, nitration and reduction) have been described in the literature. See, for example, Holt et al U.S. Pat. No. 2,174,513; Robota et al U.S. Pat. No. 3,234,292; Ligett U.S. Pat. No. 2,654,789; Heyna Ger. 637,318; Kageyama et al, Kogyo Kagaku Zasshi, 65, pp. 1203-07 (1962); Jones, J.Am. Chem. Soc., 69, pp. 2346-50 (1947). Kosak, Annals of New York Academy of Science, 172, pp. 175-85 (1970); German Offen. No. 3017542; EPO Application No. 0 038 465; EPO Application No. 0 054 464. The processes of the foregoing references have not led to a smooth and economical overall process for producing OABT in high yields with low off-isomer contamination.
Accordingly, it is an object of the present invention to provide a process for the smooth and efficient conversion of benzotrifluoride to ortho-aminobenzotrifluoride which lends itself to commercial production methods.
It is a further object of the present invention to provide a multi-step process for the conversion of benzotrifluoride to ortho-aminobenzotrifluoride which achieves high OABT yields with lower contamination by the meta-aminobenzotrifluoride (MABT) isomer.